Heretofore, there has been known a transfer conveyer in which a pair of guide rails respectively provided with guide surfaces for guiding both side surfaces of a transferred article in a transfer direction are extended in the transfer direction and in which plural pulleys are provided for circulatably supporting endless belts, which support both side lower surfaces of the transferred article, to transfer the same in the transfer direction. In an electronic component mounding apparatus or the like with such a transfer conveyer, since plural transfer conveyers are juxtaposed with the space between two adjoining transfer conveyers being set to several millimeters, care must be taken so that apparatus are not brought into contact or collision with each other when installed or displaced for new building, the layout change or the like of the facilities, and this results in making the work troublesome and taking a long time. Another conveyer has also been known, in which in order to solve this problem, end portions of the guide rails are made stretchable to be adapted easily for the displacement of the apparatus. For example, Japanese unexamined, published patent application 2000-142944 describes a stretchable transfer conveyer, in which a channeled portion is formed at an end portion of each of guide rails while another channeled portion complementarily insertable thereinto is formed at a mating end portion of each of adjuster guide rails and in which each adjuster guide rail is joined with the end portion of each guide rail to be positionally adjustable within an area in which both of the channeled portions are fitted in each other, so that protrusion portions of either one of the channeled portions insertable mutually exist to function as guides for guiding the either side of the transferred article.
However, in the stretchable transfer conveyer described in the Japanese unexamined, published patent application 2000-142944, although the protrusions of either one of the channeled portions each fitted into the other resides in the transfer direction in the stretched state, clearances are made between the protrusions and the channels to bring about discontinuity, and steps are made between the ends of the protrusions of one of the guide rail and the adjuster guide rail and the ends of the protrusions of the other guide rail. Thus, a problem arises in that the transferred article cannot be guided smoothly. Further, in the case of a transferred article thin in thickness like printed board or the like, it has been difficult to provide the channeled portions at respective ends of the guide rail and the adjuster guide rail within the thickness of the thin transferred article.
In particular, where printed boards are to be transferred, the clearance between each side surface of the printed board and a guide surface therefore is set to a range of 0.5 to 1 mm, and thus, it is necessary that each guide surface be continuous and smooth over the entire length of the transfer conveyer. Since the printed board before reflow processing holds electronic components by means of the viscosity only of soldering paste, such printed board has to be transferred smoothly without suffering any shock. However, the prior art stretchable transfer conveyer constitutes discontinuous guide surfaces and thus, is unsuitable for use in transferring such printed boards.
The present invention is made to solve the problems involved in the prior art and provides a stretchable transfer conveyer and a method of stretching a transfer conveyer wherein guide surfaces for guiding side surfaces of a transferred article can be formed as continuous and even flat surfaces even where an end portion of each guide rail is stretched by a stretching mechanism.